Method for manufacturing a thermopile on a membrane and a membrane-less thermopile, the thermopile thus obtained and a thermoelectric generator comprising such thermopiles

ABSTRACT

A method for manufacturing thermopile carrier chips comprises forming first type thermocouple legs and second type thermocouple legs on a first surface of a substrate and afterwards removing part of the substrate form a second surface opposite to the first surface, thereby forming a carrier frame from the substrate and at least partially releasing the thermocouple legs from the substrate, wherein the thermocouple legs are attached between parts of the carrier frame. First type thermocouple legs and second type thermocouple legs may be formed on the same substrate or on a separate substrate. In the latter approach both types of thermocouple legs may be optimised independently. The thermocouple legs may be self-supporting or they may be supported by a thin membrane layer. After mounting the thermopile carrier chips in a thermopile unit or in a thermoelectric generator, the sides of the carrier frame to which no thermocouple legs are attached are removed. A thermoelectric generator according to the present disclosure may be used for generating electrical power, for example for powering an electrical device such as a watch. It may be used with a heat source and/or heat sink with high thermal resistance, such as a human body.

TECHNICAL FIELD

The present disclosure relates to thermopiles and to thermoelectricgenerators (TEGs) for scavenging of ambient energy, and morespecifically to TEGs operated with a heat source and/or with a heat sinkhaving a large thermal resistance, e.g. to TEGs operated underconditions of non-constant heat flow and non-constant temperaturedifference. The disclosure also relates to a method of manufacturingthermopiles suited for applications on a heat source or a heat sink withhigh thermal resistance, e.g. on a human body or on a body of any otherendotherm. The disclosure furthermore relates to applications where aTEG dissipates heat into a fluid with high thermal resistance such asfor example air or receives heat from a fluid with high thermalresistance such as for example air, having a different temperature withrespect to the heat source and/or the heat sink where the TEG ispositioned.

BACKGROUND

A thermoelectric generator (TEG) utilises a temperature differenceoccurring between a hot (warm) object, i.e. a heat source, and itscolder surrounding, i.e. a heat sink, and is used to transform aconsequent heat flow into a useful electrical power. The necessary heatcan be produced by radioactive materials, as e.g. in space applications,or by sources available in the ambient, like e.g. standardcooling/heating systems, pipe lines including pipe lines with warm wastewater, surfaces of engines, parts of machinery and buildings or byendotherms (i.e. by warm-blooded animals including human beings andbirds, as well as by other endotherms). Natural temperature gradientsalso could be used, such as geothermal temperature gradients andtemperature gradients on ambient objects when naturally heating/coolingat day/night, etc.

There is a growing commercial interest in small-size TEGs, which couldreplace batteries in consumer electronic products operating at low powerand in autonomous devices. For example, TEGs mounted in a wristwatchhave been used to generate electricity from wasted human heat, thusproviding a power source for the watch itself, see M. Kishi, H. Nemoto,T. Hamao, M. Yamamoto, S. Sudou, M. Mandai and S. Yamamoto in“Micro-Thermoelectric Modules and Their Application to Wristwatches asan Energy Source”, Proceedings ICT'99 18^(th) Int. Conference onThermoelectrics, p. 301-307, 1999. Also, the first wireless sensor nodesfully powered by TEGs have been practically demonstrated andsuccessfully tested on people as reported by V. Leonov, P. Fiorini, S.Sedky, T. Torfs and C. Van Hoof in “Thermoelectric MEMS generators as apower supply for a body area network”, Proceedings of the 13thInternational Conference on Solid-State Sensors, Actuators andMicrosystems (Transducers'05), Seoul, Korea, Jun. 5-9, 2005, pp.291-294; by B. Gyselinckx, C. Van Hoof, J. Ryckaert, R. Yazicioglu, P.Fiorini and V. Leonov in “Human++: Autonomous Wireless Sensors for BodyArea Networks”, Proc. of the Custom Integrated Circuit Conference(CICC'05), 2005, pp. 13-19; and by V. Leonov and R. Vullers in “WirelessMicrosystems powered by homeotherms”, Proc. Smart Systems IntegrationConference, Paris, 27-28 Mar. 2007. Also the first practically usefuldevice for medical applications, a wireless pulse oximeter, has beendemonstrated which is fully powered by a wrist TEG and does not containany battery as reported by T. Torfs, V. Leonov, B. Gyselinckx and C. VanHoof in “Body-Heat Powered Autonomous Pulse Oximeter”, Proc. of the IEEEInt. Conf. on Sensors, Daegu, Korea, 22-25 Oct. 2006, see also inAbstract book, p. 122.

Recently, MEMS technology has also been used to fabricate miniaturisedthermopiles, as described by M. Strasser, R. Aigner, C. Lauterbach, T.F. Sturm, M. Franosh and G. Wachutka in “Micromachined CMOSThermoelectric Generators as On-chip Power Supply”, Transducers '03.12^(th) International Conference on Solid State Sensors, Actuators andMicrosystems, p. 45-48, 2003 (Infineon Technologies); by A. Jacquot, W.L. Liu, G. Chen, J.-P. Fleurial, A. Dausher, B. Lenoir in “Fabricationand modeling of an in-plane thermoelectric micro-generator”, ProceedingsICT'02. 21^(st) International Conference on Thermoelectrics, p. 561-564,2002; and by H. Bötner, J. Nurnus, A. Gavrikov, G. Kühner, M. Jägle, C.Künzel, D. Eberhard, G. Plescher A. Schubert and K.-H. Schlereth in “NewThermoelectric Components using Microsystem Technologies”, Journal ofMicroelectromechanical Systems, vol. 13, no. 3, p. 414-420, 2004.

Recently, thin film technology has also been used to fabricateminiaturised TEGs on a thin polymer tape, as described by S. Hasebe, J.Ogawa, M. Shiozaki, T. Toriyama, S. Sugiyama, H. Ueno and K. Itoigawa in“Polymer based smart flexible thermopile for power generation”, 17thIEEE Int. Conf. Micro Electro Mechanical Systems (MEMS), 2004, pp.689-692; by I. Stark and M. Stordeur in “New micro thermoelectricdevices based on bismuth telluride-type thin solid films”, Proceeding ofthe 18^(th) International Conference on Thermoelectrics (ICT),Baltimore, 1999, p. 465-472; and by I. Stark in “Thermal EnergyHarvesting with Thermo Life®”, Proceedings of International Workshop onWearable and Implantable Body Sensor Networks (BSN'06), 2006.

Recently, thin-film technology has also been used to fabricateminiaturised thermopiles on a membrane, where the membrane is a thinlayer of material suspended on and sustained by a carrier frame, themembrane being much thinner than the carrier frame. Miniaturisedthermopiles on a membrane are e.g. described by A. Jacquot, W. L. Liu,G. Chen, J.-P. Fleurial, A. Dauscher, B. Lenoir in “Fabrication andmodelling of an in-plane thermoelectric micro-generator”, ProceedingsICT'02. 21^(st) International Conference on Thermoelectrics, p. 561-564,2002.

In the patent application US-2006-0000502, a micromachined TEG isproposed specially suited for application on heat sources having largethermal resistance, e.g., on human beings. It is proposed and shown thatan effective TEG for such applications should contain a large hot plate,a large radiator and a tall spacer somewhere in between the plates. Thedesign and technology for the first micromachined thermopiles speciallysuited for such applications are reported by V. Leonov, P. Fiorini, S.Sedky, T. Torfs and C. Van Hoof in “Thermoelectric MEMS generators as apower supply for a body area network”, Proceedings of the 13thInternational Conference on Solid-State Sensors, Actuators andMicrosystems (Transducers '05), 2005, pp. 291-294.

Recently, an effective TEG using any of the above-mentioned thermopiletypes has been proposed, with specific thermal matching arrangementsimplemented in the TEG and/or with a multi-stage arrangement of thethermopiles, offering further improvement of its performance on a heatsource or/and on a heat sink with high thermal resistance, morespecifically when the TEG is used under conditions of non-constant heatflow and non-constant temperature difference (U.S. Ser. No. 12/028,614).

TEGs can be characterised by an electrical and a thermal resistance andby both voltage and power generated per unit temperature differencebetween the hot and cold sides of the TEG. The relative importance ofthese factors depends on the specific application. In general, theelectrical resistance should be low and, obviously, voltage or poweroutput should be maximised (in particular in applications with smalltemperature difference between the heat source and the heat sink, i.e. afew degrees C. or few tens degrees C.). If a constant temperaturedifference is imposed at the boundaries of the TEG, e.g. by means of hotand cold plates at fixed temperatures relative to each other, the valueof thermal resistance is not crucial, because the output voltage and theoutput power are proportional to the temperature difference, which isfixed. Contrary thereto, if the boundary condition is a constant heatflow or a limited heat flow through the device, then the thermalresistance is of primary importance and the voltage and the powerproduced by the TEG are different from the voltage and the powerproduced under conditions of constant temperature difference. The term“constant heat flow” means that in the considered range of TEG thermalresistances the heat flow through the device is constant (limited by theambient). However, this does not mean that the heat flow stays at thesame value over time in a practical application. The term “limited heatflow” means that when decreasing the thermal resistance of the TEG, theheat flow through the device increases till a certain value, at whichthe conditions of constant heat flow are reached. In the case of“limited heat flow” the heat flow through the device is not limited bythe ambient, but is limited for example by the thermal resistance of theTEG.

The basic element of a TEG is a thermocouple 10 (FIG. 1). An example ofa thermocouple 10 comprises a first thermocouple leg 11 and a secondthermocouple leg 12 formed of two different thermoelectric materials,for example of the same but oppositely doped semiconductor material andexhibiting low thermal conductance and low electrical resistance. Forexample, the thermocouple legs 11, 12 could be formed from BiTe. If thefirst thermocouple leg 11 is formed of n-type BiTe, then the secondthermocouple leg 12 may be formed of p-type BiTe, and vice versa. Thethermocouple legs 11, 12 are connected by an electrically conductiveinterconnect, e.g. a metal layer interconnect 13, which forms alow-resistance ohmic contact to the thermocouple legs 11, 12. The pointsof contact in between the legs 11, 12 and interconnects 13 are calledthermocouple junctions.

In FIG. 2, a TEG 20 comprising a thermopile 21 comprising a pluralityof, preferably a large number of thermocouples 10, is shown. Thethermopile 21 is sandwiched in between a hot plate 22 and a cold plate23. The hot plate 22 and the cold plate 23 are made of materials havinga large thermal conductivity, so that the thermal conductance of theplates 22, 23 is much larger (at least by a factor of 10) than the totalthermal conductance of the thermopile 21.

In case of a heat source or/and a heat sink with high thermalresistance, three types of thermopiles and their arrangement in a TEGmay be considered as suitable: (1) commercial small-size thermopilesarranged in a multi-stage structure according to U.S. Ser. No.12/028,614, (2) a micromachined thermopile on a raised elongatedstructure or on a spacer according to US-2006-0000502, (3) a thermopileon a polymer tape arranged as e.g. reported by Ingo Stark and P. Zhou inWO 2004/105143, by Ingo Stark in US 2006/0151021 and by 1. Stark and M.Stordeur in “New micro thermoelectric devices based on bismuthtelluride-type thin solid films”, Proceeding of the 18^(th)International Conference on Thermoelectrics (ICT), 1999, p. 465-472.Membrane-type thermopiles with a thermal difference between the centerof the membrane and its side frame (A. Jacquot, W. L. Liu, G. Chen,J.-P. Fleurial, A. Dauscher, B. Lenoir in ‘Fabrication and modeling ofan in-plane thermoelectric micro-generator’, Proceedings ICT'02. 21stInternational Conference on Thermoelectrics, p. 561-564, 2002) are notappropriate for applications on a heat source and/or on a heat sink withhigh thermal resistances because of their thermal mismatch (due to theirsmall contact area with the heat source or the heat sink), andconsequently the too low voltage and power they would produce.

SUMMARY

It is an object of the present disclosure to provide a method formanufacturing good thermopile chips, thermopile units and TEGs with suchthermopile chips for applications on a heat source and/or on a heat sinkwith high thermal resistance. Thermopiles manufactured according to thepresent disclosure comprise thermocouples that may be supported by amembrane layer or that may be self-supporting. The thermocouples mayhave dimensions so as to be flexible, e.g. bendable. Due to thisflexibility, the thermocouples may be shock absorbing, leading to alower risk of damage to the thermocouples as compared to prior artdevices, e.g. micromachined devices. The thermocouple legs of thermopilechips according to the present disclosure may be wider and/or longerthan in prior art devices, leading to a cheaper technology beingavailable for manufacturing such thermocouple legs. Moreover, better andmore reliable electrical contacts may be obtained in thermopile chipsaccording to the present disclosure. Thermopile chips according to thepresent disclosure may have a reduced sensitivity to dust duringmanufacturing as compared to prior art methods. Therefore the method formanufacturing thermopile ships according to the present disclosure mayhave a good manufacturing yield. Furthermore, a good quality ofthermoelectric material may be obtained and both types of thermoelectricmaterial may be optimised independently.

In a first aspect, the present disclosure provides a method formanufacturing a thermopile carrier chip comprising a plurality ofthermocouples, the method comprising: providing on a first surface of afirst substrate a plurality of first type thermocouple legs; thereafterforming a first carrier frame from the first substrate by removing partof the first substrate from a second surface opposite to the firstsurface, the first carrier frame comprising a first hot carrier part, afirst cold carrier part and first removable beams, thus at leastpartially releasing the first type thermocouple legs from the firstsubstrate, the first type thermocouple legs being attached between thefirst hot carrier part and the first cold carrier part; and electricallyconnecting the plurality of first type thermocouple legs with aplurality of second type thermocouple legs, thereby forming anelectrical series connection of alternating first type thermocouple legsand second type thermocouple legs.

According to the present disclosure, electrically connecting theplurality of first type thermocouple legs with a plurality of secondtype thermocouple legs may comprise providing on the first surface ofthe first substrate a plurality of second type thermocouple legs,wherein the plurality of second type thermocouple legs are attachedbetween the first hot carrier part and the first cold carrier part.Alternatively, according to the present disclosure, electricallyconnecting the plurality of first thermocouple legs with a plurality ofsecond type thermocouple legs may comprise: providing on a first surfaceof a second substrate a plurality of second type thermocouple legs andthereafter forming a second carrier frame from the second substrate byremoving part of the second substrate form a second surface opposite tothe first surface, the second carrier frame comprising a second hotcarrier part, a second cold carrier part and second removable beams,thus at least partially releasing the second type thermocouple legs fromthe second substrate, the second type thermocouple legs being attachedbetween the second hot carrier part and the second cold carrier part. Itis an advantage of providing the first type thermocouple legs on a firstsubstrate and the second type thermocouple legs on a second substratethat the quality of both types of thermocouple legs may be improved oreven optimised independently.

The method of the present disclosure may furthermore comprise, beforeproviding the plurality of first and/or second type thermocouple legs onthe first surface of the first and/or second substrate, providing anelectrically insulating membrane layer onto that surface of the firstand/or second substrate.

The method may furthermore comprise separating the membrane layer fromthe first and/or second removable beams. Separating the membrane layerfrom the first and/or second removable beams may comprise providingwindows in the membrane layer, for example by dry etching, or it maycomprise cutting, e.g. laser cutting, the membrane layer.

The method of the present disclosure may furthermore comprise providingat least one thermal shunt for thermally connecting one side of theplurality of thermocouples to the first and/or second hot carrier partand/or for thermally connecting the other side of the plurality ofthermocouples to the first and/or second cold carrier part.

The method may furthermore comprise removing the first and/or secondremovable beams of the first and/or second carrier frame. Removing thefirst and/or second removable beams may for example be donemechanically, e.g. by breaking, cutting or dicing, or chemically, e.g.by etching.

In a second aspect, the present disclosure provides a method formanufacturing a thermopile unit, wherein the method comprisesmanufacturing at least one thermopile carrier chip according to thefirst aspect of the present disclosure, assembling the at least onethermopile carrier chip into a thermopile unit and removing the firstand/or second removable beams. Assembling the at least one thermopilecarrier chip may comprise attaching at least one thermopile carrier chipto a thermally insulating structure, e.g. a thermally insulating pillaror a thermally insulating wall. Assembling the at least one thermopilecarrier chip may comprise providing at least one thermally conductivespacer thermally connected to at least one of the first and/or secondhot carrier part and the first and/or second cold carrier part.

In a third aspect, the present disclosure provides a method formanufacturing a thermoelectric generator, wherein the method comprisesmanufacturing at least one thermopile carrier chip in accordance withthe first aspect of the present disclosure or a thermopile unit inaccordance with the second aspect of the present disclosure, andproviding the at least one thermopile carrier chip or thermopile unitbetween a hot plate and a cold plate.

The method for manufacturing a thermoelectric generator according to thepresent disclosure may furthermore comprise providing at least onethermally insulating structure between the hot plate and the cold plate.

The at least one thermopile carrier chip or thermopile unit may beplaced parallel to the hot plate and/or parallel to the cold plate. Theat least one thermopile carrier chip or thermopile unit may be placed inan inclined position with respect to the hot plate and/or the coldplate.

In a fourth aspect, the present disclosure furthermore provides athermopile chip comprising a plurality of thermocouple legs which arethermally coupled in parallel, and a carrier frame comprising at least ahot carrier part and a cold carrier part, the thermocouple legs beingattached between the hot carrier part and the cold carrier part andbeing at least partially released from a substrate from which the hotcarrier part and the cold carrier part are made.

A thermopile chip according to the fourth aspect of the presentdisclosure may be obtained after removing the removable beams from atleast one thermopile carrier chip, e.g. a thermopile carrier chipmanufacture according to the first aspect of the present disclosure. Ona thermopile carrier chip, thermocouple legs of a first type may beprovided. Thermocouple legs may for example be n-type or p-type. Forexample, on one thermopile carrier chip only thermocouple legs of afirst type may be provided, and on another thermopile carrier chipthermocouple legs of a second type different from the first type may beprovided. Two such thermopile carrier chips may then be electricallyconnected together so as to from an electrical series connection ofalternating first type and second type thermocouple legs, thethermocouple legs being thermally connected in parallel. Alternatively,both first type and second type thermocouple legs may be provided on asame thermopile carrier chip. In this case again the thermocouple legsare connected so as to form an electrical series connection ofalternating first type and second type thermocouple legs, whilethermally providing a parallel connection.

A thermopile chip according to the present disclosure may comprise anelectrically insulating membrane layer at least partially supporting theplurality of thermocouple legs. In a particular embodiment the thermalconductance of the electrically insulating membrane layer may besubstantially smaller than the sum of the thermal conductance of theplurality of thermocouple legs.

The thermopile chip may comprise thermocouple legs having athermoelectric part and an electrically conductive part, wherein theelectrically insulating membrane layer is present underneath thethermoelectric part and/or underneath the electrically conductive part.

The plurality of thermocouple legs may comprise a hot junction and acold junction, wherein the distance between the hot junction and thecold junction is substantially smaller than the distance between the hotcarrier part and the cold carrier part.

A thermopile chip according to the present disclosure may furthermorecomprise at least one thermal shunt forming a thermal connection betweenthe cold junction of the plurality of thermocouple legs and the coldcarrier part and/or between the hot junction of the plurality ofthermocouple legs and the hot carrier part. The at least one thermalshunt may form an electrical connection between adjacent thermocouplelegs.

In a fifth aspect, the present disclosure provides a thermopile unitcomprising at least one thermopile chip according to the fourth aspectof the present disclosure. A thermopile unit may comprise a plurality ofthermopile chips being connected with their hot carrier parts to eachother and with their cold carrier parts to each other. The plurality ofthermopile chips may be connected to each other by means of thermallyinsulating material. The thermopile chips may have a front side and aback side, and the plurality of thermopile chips may for example beconnected in pairs with their back sides towards each other. There maybe an electrically insulating spacer in between two adjacent pairs ofthermopile chips.

A thermopile unit in accordance with the present disclosure mayfurthermore comprise a thermally insulating structure between the hotcarrier parts and the cold carrier parts. It may further comprise atleast one thermally conductive spacer for thermally connecting the atleast one thermopile chip to a heat source and/or to a heat sink.

In a sixth aspect, the present disclosure furthermore provides athermoelectric generator comprising at least one thermopile chip inaccordance with the fourth aspect of the present disclosure or at leastone thermopile unit in accordance with the fifth aspect of the presentdisclosure, placed between a hot plate for providing thermal connectionwith a heat source and a cold plate for providing thermal connectionwith a heat sink. A thermoelectric generator in accordance with thepresent disclosure may comprise at least one thermally insulatingstructure, e.g. thermally insulating pillar or thermally insulatingwall, between the hot plate and the cold plate. The at least onethermopile chip or thermopile unit may for example be placed parallel tothe hot plate and/or parallel to the cold plate. The at least onethermopile chip or thermopile unit may be placed in an inclined positionwith respect to the hot and/or cold plate. The thermoelectric generatormay be filled at least partially with a thermally insulating material.

A thermoelectric generator according to the present disclosure may beused for generating electrical power, for example for powering anelectrical device such as e.g. a watch. A thermoelectric generatoraccording to the present disclosure may be used with a heat sourceand/or a heat sink with a high thermal resistance, e.g. wherein the heatsource is a human being, a clothed human being, an animal or ambient airand/or wherein the heat sink is a human being, a clothed human being, ananimal or ambient air.

These and other characteristics, features and advantages will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, which illustrate, by way of example, theprinciples of the invention. This description is given for the sake ofexample only, without limiting the scope of the invention. The referencefigures quoted below refer to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a thermocouple comprising ann-type and a p-type semiconducting thermocouple leg and conductiveinterconnects, e.g. metal layer interconnects.

FIG. 2 is a schematic illustration of a simple TEG comprising a largenumber of thermocouples sandwiched in between a hot plate and a coldplate.

FIG. 3 is a 3D-view of a thermopile chip after removing the removablebeams from the carrier frame.

FIG. 4 is a cross-sectional general view of the TEG, comprising theassembly of a thermopile unit with hot and cold plates.

FIG. 5 is a 3D-view of a TEG, showing the assembly of a thermopile unitwith hot and cold plates wherein a thermally insulating wall andthermally insulating pillars are installed.

FIG. 6 is a 3D-view of a TEG comprising a thermopile unit with twothermopile chips, after removal of the removable beams from the carrierframe.

FIG. 7 shows the thin/thick film thermocouple as a basic element of athermopile according to principles described herein.

FIG. 8 a shows a thermopile carrier chip upon its fabrication, beforeremoval of the removable beams from the carrier frame.

FIG. 8 b shows a thermopile chip upon its installation into a thermopileunit or into a TEG, after removal of the removable beams from thecarrier frame.

FIGS. 9 a-d illustrate Part I of the fabrication process for apolycrystalline SiGe thermopile chip.

FIGS. 10 a-c illustrate Part I of the fabrication process for a BiTethermopile chip.

FIGS. 11 a,b illustrate Part II of the fabrication process of athermopile chip.

FIG. 12 shows etched grooves on the back side of a thermopile chip foreasy and controlled breaking of the removable beams from the carrierframe after its installation into a thermopile unit or into a TEG.

FIG. 13 shows a thermopile chip, fabricated as shown in FIG. 12, afterbreaking the removable beams from the carrier frame on the etchedgrooves.

FIG. 14 a-c show the cross section of thermopile carrier chips, in whicha bulk etch of the substrate is performed in different ways: (a)anisotropic etching, (b) isotropic etching, and (c) deep reactive ionetching.

FIG. 15 is a 3D-view of a TEG with thermopile carrier chips beforeremoval of the removable beams from the carrier frame.

FIG. 16 shows a side view of a thermopile unit, supported by attachedthermally insulating pillars or walls, before breaking the removablebeams from the carrier frame.

FIG. 17 shows a side view of a thermopile unit after breaking theremovable beams from the carrier frame.

FIG. 18 shows the general design of a thermopile unit with thermallyconductive pillars installed thermally in series to the thermopilechips.

FIG. 19 shows an example of thermopile unit with thermally conductivespacers or pillars installed thermally in series to the thermopilechips.

FIG. 20 shows a thermopile unit with coupled thermopile chips, whereinthe two chips in each chip couple are facing with their back sides toeach other.

FIG. 21 illustrates the effect of thermal shunts used to decouple thedistance between the hot carrier part and the cold carrier part of athermopile chip from the distance over which the main temperature dropoccurs.

FIG. 22 shows a thermopile chip with thermal shunts made of electricallyand thermally conductive material between the thermocouple legs and thesides of the carrier frame. The shunts perform also the function ofelectrical interconnection of two adjacent thermocouple legs.

FIG. 23 shows a side view of a thermopile chip with thermal shunts madeof thermally conductive material, while electrical interconnects aremade of electrically conductive material.

FIG. 24 shows a thermopile chip with thermal shunts made of materialthat is thermally conductive but not electrically conductive.

FIG. 25 shows a side view of a thermopile chip with thermal shunts as inFIG. 24, in which a membrane is only present in the area of thermocouplelegs, i.e. under the legs and in between them.

FIGS. 26 a-e show examples of a thermopile chip structure: FIG. 26 a andFIG. 26 b illustrate a thermopile chip without membrane for supportingthe thermal shunts, electrical interconnects and/or thermocouple legs;FIG. 26 c shows a side view of a membrane-less thermopile chip withelectrically conductive thermal shunts; FIG. 26 d shows a side view of amembrane-less thermopile chip with electrically conductive thermalshunts, but fabricated on an electrically insulating substrate; FIG. 26e shows a side view of a silicon thermopile chip, wherein a doped layerof silicon serves as an etch stop barrier and also serves as a thermalshunt.

FIG. 27 shows one of two thermopile chips to be bonded and electricallyconnected to another chip (with opposite type of conductivity) as shownin FIG. 28.

FIG. 28 shows the second thermopile chip to be bonded and electricallyconnected to the chip shown in FIG. 27. If the first chip is p-type, thesecond one is n-type and vice versa.

FIG. 29 shows the two coupled thermopile carrier chips of FIG. 27 andFIG. 28. For illustration purposes, the chips are shownsemi-transparent.

FIG. 30 illustrates an additional possible method of fabrication of athermopile chip.

FIG. 31 a and FIG. 31 b show diced thermopile chips as in FIG. 30 afterpermanent or temporary (e.g. only for technological reasons) attachmentof side pillars.

FIG. 32 illustrates an alternative way of separation of the membranefrom the removable beams.

FIG. 33 shows the result of removing the removable beams from thethermopile carrier chip shown in FIG. 32.

FIG. 34 shows the dependence of the output power on the length of thethermocouple legs and of a membrane for a TEG according to FIG. 13, with14 thermopile chips and with no thermal shunts, for a first TEG design.

FIG. 35 shows the dependence of the output power on the length of thethermocouple legs and of a membrane for a TEG according to FIG. 13, with10 thermopile chips and with no thermal shunts, for a second TEG design.

FIG. 36 shows the dependence of the output power on the length of amembrane for a TEG according to FIG. 22, with 14 thermopile chips andwith thermal shunts, for a third TEG design.

FIG. 37 shows the dependence of the output power on the length of thethermocouple legs for a TEG according to FIG. 22, with 14 thermopilechips and with thermal shunts, for the third TEG design.

FIG. 38 shows the dependence of the output power on the length of amembrane for a TEG according to FIG. 22, with 10 thermopile chips andwith thermal shunts, for a fourth TEG design.

FIG. 39 shows the dependence of the output power on the length of thethermocouple legs for a TEG according to FIG. 22, with 10 thermopilechips and with thermal shunts, for the fourth TEG design.

FIG. 40 shows an example of an integration of thermopile chips into awatch.

FIG. 41 shows an example of an integration of thermopile chips into awatch.

FIG. 42 shows an arrangement wherein a thermopile chip is mountedparallel to the hot plate or the cold plate of a TEG. As an example, twothermally insulating pillars are shown to hold one of the chip sides.

FIG. 43 shows an arrangement wherein a thermopile chip is mountedparallel to the hot plate or the cold plate of a TEG. As an example, athermally insulating wall is shown to hold one of the chip sides.

FIG. 44 illustrates an arrangement wherein a thermopile chip is mountedparallel to the cold plate of a TEG. As an example, the hot plate has anon-flat complex shape, while two thermally insulating pillars (only oneis seen; the other is behind the cold plate) are to hold one of the chipsides. The other side, as an example, is being held by a pillar.

FIG. 45 illustrates an example of an arrangement wherein a thermopilechip is mounted parallel to the hot plate and the cold plate of a TEG,wherein two thermally insulating walls hold both sides of the chip.

FIG. 46 illustrates an arrangement wherein a thermopile chip is mountednon-parallel with and non-orthogonal to both the hot plate and the coldplate of a TEG.

FIG. 47 shows a diced thermopile chip containing four thermopilesintended for an arrangement of the chip parallel to the hot plate andthe cold plate in a thermopile unit or in a TEG.

FIG. 48 a-c illustrate an example of the assembly of a thermopile chipas shown in FIG. 47 with the hot plate and the cold plate of athermopile unit, of a TEG, or of a product: (a) a thermopile chipinstalled on a shaped hot plate with thermally insulating cylindricalpillars holding the chip during removal of the removable beams; (b)possible final view of the assembly of the thermopile chip with the coldand hot plates; (c) another possible final view of the assembly of thethermopile chip with the cold and hot plates wherein the thermallyinsulating elements are removed and wherein the position of the platesis fixed by thermally insulating pillars or walls (not shown) or by apart of a product in which the TEG is embedded.

FIG. 49 shows a TEG with the inner space filled with thermallyinsulating material, the material preferably having a thermalconductivity less than the thermal conductivity of air. Several ways,with air gaps and without such gaps are shown.

FIG. 50 shows an example of a way of mounting two thermopile chipsbonded to each other, e.g., in case of a separate p-type chip and n-typechip.

FIG. 51 shows an example of a product, e.g. a watch, with an arrangementof a thermopile chip parallel to the hot plate and the cold plate.

FIG. 52 shows a micromachined thermocouple with thermal shunts accordingto the present disclosure.

FIG. 53 shows a micromachined thermocouple with thermal shunts accordingto the present disclosure.

FIG. 54 shows a micromachined thermocouple with thermal shunts accordingto the present disclosure.

FIG. 55 shows two adjacent micromachined thermocouples with thermalshunts and wherein a die comprises pillars or bumps to increase anaverage distance in between both dies.

FIG. 56 shows a micromachined thermocouple with thermal shunts inbetween the thermocouples and a die.

In the different figures, the same reference signs refer to the same oranalogous elements.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The present invention will be described with respect to particularembodiments and with reference to certain drawings but the invention isnot limited thereto. The drawings described are only schematic and arenon-limiting. In the drawings, the size of some of the elements may beexaggerated and not drawn on scale for illustrative purposes. Thedimensions and the relative dimensions do not necessarily correspond toactual proportions and reductions to practice of the invention.

Furthermore, the terms first, second, third and the like in thedescription, are used for distinguishing between similar elements andnot necessarily for describing a sequential or chronological order. Itis to be understood that the terms so used are interchangeable underappropriate circumstances and that the embodiments described herein arecapable of operation in other sequences than described or illustratedherein.

It is to be noticed that the term “comprising” should not be interpretedas being restricted to the means listed thereafter; it does not excludeother elements or steps. Thus, the scope of the expression “a devicecomprising means A and B” should not be limited to devices consistingonly of components A and B.

A thermopile chip 30 according to an embodiment is illustrated in FIG. 3(3D-view). The thermopile chip 30 comprises a large number ofthermocouples 10 manufactured on a membrane 34 using a thin or thickfilm technology. In this context a thin film is defined as a film with athickness not exceeding 2 μm, and a film thicker than 2 μm is consideredas a thick film. Each thermocouple 10 comprises two thermocouple lines,each thermocouple line comprising a thermoelectric part 31 or athermocouple leg 31 and an interconnect 32. The thermoelectric parts 31or thermocouple legs 31 of one thermocouple 10 are made of two differentthermoelectric materials, for example a p-type semiconductor materialfor one of the thermocouple legs and an n-type semiconductor materialfor the other thermocouple leg. Both thermocouple legs may for examplebe made of a bismuth telluride group material. Other thermoelectricmaterials may be used. The interconnect 32 may be a metal layer or maycomprise the same thermoelectric materials as the thermoelectric parts31 covered with a metal layer, or may have a metal layer underneath thethermoelectric material. The membrane 34 may be connected to a carrierframe with sides 33, for example a silicon carrier frame, which may beselected because of its high thermal conductivity and compatibility withmodern microelectronic technologies. The membrane 34, e.g. a siliconnitride membrane, interconnects the hot side 35 of the thermopile chip30 and its cold side 36. The hot side 35 will be referred to below asthe hot carrier part 35, while the cold side 36 will be referred tobelow as the cold carrier part 36. The membrane 34 may be made of anytechnologically compatible material such as for example SiO₂,Si_(x)N_(y)-on-SiO₂, polymers, etc.

A TEG 40 may comprise a thermopile unit 50 (FIG. 4) comprising at leastone thermopile chip 30, wherein the thermocouples 10 are connectedelectrically in series and thermally in parallel. The thermopile unit 50may be placed in between plates 37 and 38. In a preferred embodiment,the thermopile chips 30 in a thermopile unit 50 may be connectedelectrically in series and thermally in parallel. However, otherconfigurations are possible, such as for example a combination ofseries/parallel connections, electrically or thermally or bothelectrically and thermally. The thermopile chips 30 may be mountedparallel to the plates 37, 38, orthogonal to the plates 37, 38 or in aninclined position with respect to the plates 37, 38. Either of theplates 37, 38 is called a hot plate. The other one then has a lowertemperature than the first one and thus is called a cold plate. For thesake of simplicity, plate 37 will be further referred to as the hotplate 37 and plate 38 will be referred to as the cold plate 38. Thethermopile unit 50 may further comprise other elements, such as forexample thermal insulation 51, a radiator or any other structuresdecreasing the interface thermal resistance to the ambient. The thermalinsulation 51 may represent vacuum, air or any other thermallyinsulating material, and may include thermally insulating pillars 54and/or thermally insulating encapsulating structures/walls 55,completely or partially surrounding the inner volume in between the hotplate 37 and the cold plate 38, as shown in FIG. 5, where the plate 37is shown transparent for clarity of presentation. Instead of a plate 37and/or 38, a radiator similar to the one illustrated in US-2006-0000502and U.S. Ser. No. 12/028,614 may be used, the entire disclosures ofwhich are incorporated herein by reference. The hot plate 37 and/or thecold plate 38 may also be replaced with any other structure decreasingthe interface thermal resistance to the ambient, i.e. to the heat sourceand/or the heat sink. For example, the hot plate 37 of a TEG 40 forapplication on the skin of an endotherm may feature micro- ornano-needles penetrating a certain distance into the skin.

A TEG 40 may comprise one or more thermopile chips 30 placed for examplein between and orthogonal to the hot plate 37 and the cold plate 38, asshown in FIG. 6. In FIG. 6 two thermopile chips 30 are shown as anexample. The hot plate 37 and the cold plate 38 may be supported by atleast one thermally insulating pillar 54 and/or at least one thermallyinsulating wall 55. The hot carrier part 35 serves as a thermallyconductive spacer, separating the thermopiles from the hot plate 37, andthe cold carrier part 36 serves as a thermally conductive spacer,separating the thermopiles from the cold plate 38. These thermallyconductive spacers are equivalent to the spacers and to the raisedelongated structures as disclosed in US-2006-0000502, the entiredisclosure of which is incorporated herein by reference.

In a further aspect, an example of a process for manufacturing athermopile chip 30 and a TEG 40 is described below. FIG. 7 comprises aside view and a top view of part of a thermopile chip 30, showing onethermocouple as a basic element of a thermopile chip. As an example asilicon-based technology is considered, wherein a thermocouple 10comprises two thermocouple lines 71, 72 (FIG. 7). The thermocouple lines71, 72 comprise a thermoelectric layer 73 and an electrically conductivelayer, e.g. a metal layer 74. It is assumed, as an example only, thatone thermocouple line 71 comprises a p-type bismuth telluridethermoelectric material, and that the other thermocouple line 72comprises a n-type bismuth telluride thermoelectric material. At one endthe lines 71, 72 are electrically interconnected by means of anelectrically conductive connection 32, e.g. a metal layer, while at theother end they are interconnected with the neighbouring thermocouples orwith output leads. The parts 11, 12 of the thermopile lines 71, 72,being parts only comprising thermoelectric material 73 and notcomprising an electrically conductive layer, e.g. metal layer 74, serveas thermocouple legs or as thermoelectric parts 31. The other parts ofthe thermocouple lines 71, 72, the interconnects between them and thecontacts to the neighbouring thermocouples may be coated with anelectrically highly conductive layer, e.g. a metal layer, withoutunderlying thermoelectric layer, e.g. bismuth telluride layer, and thusare considered as interconnects 32. In FIG. 7 the thermoelectric layer73 is shown underneath the metal layer 74 (between the membrane 34 andthe metal layer 74) however it may be on top of the metal layer 74 aswell.

The TEG fabrication may be divided into three parts. In Part I, athermopile wafer 28 is fabricated using deposition (e.g. chemical vapourdeposition (CVD) or other suitable deposition techniques), lithographyand etching of various layers on a substrate, e.g. a planar substrate.The various layers may comprise for example layers of thermoelectricmaterial, metal layers and an electrically insulating layer for forminga membrane. In Part II, windows may be etched in the membrane layer,followed by bulk etching of the substrate, thereby releasing themembrane 34 and forming a thermopile carrier chip 29, e.g. a siliconcarrier chip, with a carrier frame comprising sides 33 and removablebeams 41 as shown in FIG. 8 a. The windows in the membrane layers arelocated such that they separate the membrane 34 from the removable beams41. In a last Part III, the thermopile carrier chips 29 are mounted intoa thermopile unit 50. The thermopile unit 50 is then placed in betweenthe hot plate 37 and the cold plate 38, the thermally insulating pillars54 and/or walls 55 are installed, and the removable beams 41 of thecarrier frame are removed, e.g. broken out mechanically. FIG. 8 a showsan example of a thermopile carrier chip 29 after its manufacturing andbefore its mounting in a TEG, with the removable beams 41. FIG. 8 bshows the thermopile chip 30, which is obtained after removal of theremovable beams 41. The entire fabrication process, its modificationsand peculiarities are described in more detail below.

In Part I of the fabrication process of a TEG 40, thermopile wafers 28are formed. Although the fabrication principle is the same for differentmaterials, fabrication details may depend on the thermoelectric andother materials used for forming the thermocouples 10. As an example,fabrication processes are described for thermopile wafers 28 comprisingSiGe thermocouples and for thermopile wafers 28 comprising BiTethermocouples. In case Si_(x)Ge_(y) is used as a thermoelectricmaterial, the process may be easily adapted to Si or similar materials.In case of Bi_(x)Te_(y), the process may be easily adapted toSb_(x)Te_(y), Sb_(x)Bi_(y)Te_(z), Bi_(x)Te_(y)Se_(z),Pb_(x)Te_(y)Se_(z), Bi_(x)Sn_(y)Te_(z) and similar materials. Theprinciple of the fabrication process may be more generally applied toother thermoelectric materials such as for example skutterudites,nanostructured materials, etc. The principle of the fabrication processmay furthermore be extended to materials with similar chemicalproperties.

Firstly, Part I of a fabrication process is described for a TEG 40comprising thermopile chips 30 comprising SiGe thermocouples. Thisfabrication process is for simplicity presented for one thermocouple andis illustrated in FIG. 9 a to FIG. 9 d. In each of these Figures the topview of the thermopile wafer is shown in the bottom part of the Figure,and the corresponding side view is shown in the top part of the Figure.On a substrate 80, which is preferably thermally conductive, anelectrically insulating layer 81 is provided, e.g. deposited. Thesubstrate 80 may preferably comprise Si, but may also comprise any othersuitable thermally conductive material, such as e.g. aluminium nitride,alumina ceramic, copper, or other materials with lower thermalconductivity such as glass or polymers. The substrate 80 may have athickness of between, for example, 0.03 and 1 mm. The insulating layer81 may for example comprise Si_(x)N_(y) and have a thickness in therange between 0.1 μm and 5 μm, between 0.1 μm and 3 μm, or between 0.1μm and 1 μm, for example 0.5 μm. Furthermore, the insulating layermaterial and its thickness may be selected taking into account thefeasibility of further release of the electrically insulating layer 81to form a membrane 34. Moreover, the thermal conductance of the materialforming the electrically insulating layer 81 is preferably smaller thanthe sum of the thermal conductances of all thermocouples 10 that are tobe manufactured on the substrate 80. After providing the electricallyinsulating layer 81, a thin or thick film 82 of a first thermoelectricmaterial is provided, e.g. deposited, as shown in FIG. 9 a. In theexample given, the thermoelectric material may be n- or p-type SiGe andmay be deposited by e.g. CVD or by any suitable deposition techniqueknown by a person skilled in the art. A protective layer 83 is thenprovided, e.g. deposited, and patterned as shown in FIG. 9 a. Theprotective layer 83 may for example comprise SiO₂ and may have athickness in the range between 0.1 μm and 5 μm, between 0.1 μm and 3 μm,or between 0.1 μm and 1 μm, for example 0.5 μm. Other materials may beused for forming protective layer 83 and other layer thicknesses arepossible, provided that layer 83 protects thermoelectric layer 82 frombeing damaged during further processing, e.g. during patterning of thelayer 82 of thermoelectric material, or during patterning of the layer84 of second thermoelectric material, as described below. The layer 82of first thermoelectric material is then patterned using methods knownby a skilled person and using protective layer 83 as a mask. FIG. 9 bshows the result after patterning of the layer 82 of the firstthermoelectric material.

In a next step, a film 84 of a second thermoelectric material isprovided, e.g. deposited, and patterned using a protective layer 83′ asshown in FIG. 9 c. Protective layer 83′ may for example be a photoresistlayer. The second thermoelectric material may be for example p- orn-type SiGe deposited by e.g. CVD or by any other suitable depositiontechnique. Important for the second thermoelectric material is that itstype (n or p) is opposite to the type of the first thermoelectricmaterial. For example, if the first thermoelectric material is n-SiGe,then the second thermoelectric material is p-SiGe. Protective layer 83protects the film 82 of the first thermoelectric material duringpatterning of the film 84 of the second thermoelectric material usingthe protective layer 83′ as a mask.

In a last step of Part I of the fabrication process, protective layers83 and 83′ are removed, e.g. by selective etching, and then a film 85 ofelectrically conductive interconnection material, e.g. a metal film isprovided, e.g. deposited, and patterned as shown in FIG. 9 d. The film85 of electrically conductive interconnection material, e.g. metal film,may for example comprise aluminium, copper, gold, nickel, tungsten orany other suitable metal and may be composed of one or more differentlayers. As an example, a thin layer of gold or nickel of 10 nm, a 1-3 μmthick aluminium layer on top of it and a 0.5 μm thick layer of nickel ontop of the aluminium layer may be used. Such a metal stack has a bettercontact resistance to SiGe than a single aluminium metal layer, and ithas the advantage that the aluminium is not oxidised on open air,providing better wire bonding on aged samples. As can be seen inparticular from the bottom part of FIG. 9 d, parts of the legs of thethermocouples are not covered by the electrically conductiveinterconnection material. These parts not covered by the electricallyconductive interconnection material form the thermoelectric parts 31 ofthe legs (see also FIG. 3).

Secondly, an example of Part I of the fabrication process formanufacturing thermopile chips 30 comprising Bi_(x)Te_(y) thermocouplesis described and is illustrated in FIG. 10 a to 10 c. In each of theseFigures the top view of the thermopile wafer 28 is shown in the bottompart of the Figure, and the corresponding side view is shown in the toppart of the Figure. BiTe may be deposited by e.g. sputtering,electroplating or laser ablation. The deposition methods could also becombined with each other, for example an additional electroplating stepmay be performed on an already fabricated thin BiTe film, in order toincrease its thickness to several micrometers or more without using asexpensive equipment as the equipment used during sputtering or ablation.If sputtering or laser ablation is chosen, the process may proceed asdescribed above for SiGe, except for the fact that suitable protectivelayers 83, 83′ that can be etched selectively with respect to BiTe maypreferably be used. So the material of the protective layers 83, 83′ maybe any suitable material that can be etched away by an etching compoundthat does not etch BiTe. In a particular technological processrepresented in FIG. 10 a to FIG. 10 c the protective layer 83 may beSiO₂ as in the case of SiGe thermocouples. However, as an example, inthe process represented in FIG. 10 a to FIG. 10 c it is not completelyremoved after patterning of the film 84 of the second thermoelectricmaterial and remains present in the completed device, e.g. fortechnological reasons or for reasons of controlling stress in theresulting stack of layers.

In a first step of Part I, shown in FIG. 10 a, an electricallyinsulating layer 81 is provided, e.g. deposited, on a substrate 80, forexample a thermally conductive substrate. The substrate 80 maypreferably comprise Si, but may also comprise any other suitablethermally conductive material, such as e.g. aluminium nitride, aluminaceramic, copper, or other materials with lower thermal conductivity suchas glass or polymers. The substrate 80 may have a thickness of between,for example, 0.03 mm and 1 mm. The insulating layer 81 may for examplecomprise Si_(x)N_(y) and have a thickness in the range between 0.1 μmand 5 μm, between 0.1 μm and 3 μm, or between 0.1 μm and 1 μm, forexample 0.5 μm. Furthermore, the insulating layer material and itsthickness may be selected taking into account the feasibility of furtherrelease of this layer to form a membrane 34. Moreover, the thermalconductance of the material forming the electrically insulating layer 81is preferably smaller than the sum of the thermal conductances of allthermocouples 10 that are to be manufactured on the substrate 80. Then alayer 82 of a first thermoelectric material is provided, e.g. deposited,wherein the first thermoelectric material may be for example n- orp-type Bi_(x)Te_(y) or a similar material such as e.g. Sb_(x)Te_(y) orSb_(x)Bi_(y)Te_(y), Bi_(x)Te_(y)Se_(z), Pb_(x)Te_(y)Se_(z),Bi_(x)Sn_(y)Te_(z), or other thermoelectric materials such as e.g.skutterudites, nanostructured materials etc. A protective layer 83 isthen provided, e.g. deposited, and patterned. In a next step layer 82 ispatterned using methods known by a person skilled in the art and usingprotective layer 83 as a mask. The protective layer 83 is thencompletely removed or thinned down in the areas of its subsequentcontact with the electrically conductive layer, e.g. metal layer 85,which is provided, e.g. deposited, in later stages of the process. FIG.10 a shows the thermopile wafer 28 after patterning the protective layer83 and the layer 82 of a first thermoelectric material, and afterlocally thinning the protective layer 83.

Then, a film 84 of a second thermoelectric material is provided, e.g.deposited, and patterned using a protective layer 83′, e.g. aphotoresist layer 83′, in a similar way as described in relation withFIG. 9 c. FIG. 10 b shows the thermopile wafer after deposition andpatterning of the layer 84 of second thermoelectric material and afterremoval of protective layer 83′. As an example, and as illustrated inFIG. 10 b, during etching of the layer 84 of the second thermoelectricmaterial, the protective layer 83 may be thinned down, thereby beingcompletely removed in its thinner areas but still staying in its thickerareas, while the layer 82 of first thermoelectric material may bepartially etched (thinned down) in non-protected areas.

Finally, a thin film 85 of interconnection material, e.g. a metal film85, is provided, e.g. deposited, and patterned as shown in FIG. 10 c,thereby completing Part I of the fabrication process. The film 85 ofelectrically conductive interconnection material, e.g. metal, may forexample comprise aluminium, copper, gold, nickel, tungsten or any othersuitable metal and may be composed of one or more different layers, e.g.to obtain better properties such as providing better contact resistancewith underlying layers and protecting the interconnection material fromdeterioration for example by oxidation. As can be seen in particularfrom the bottom part of FIG. 10 c, parts of the legs of thethermocouples are not covered by the electrically conductiveinterconnection material. These parts not covered by the electricallyconductive interconnection material form the thermoelectric parts 31 ofthe legs (see also FIG. 3).

Part II of the fabrication process is shown in FIG. 11 a and FIG. 11 b,FIG. 11 a showing a top view of the thermopile wafer 28 and FIG. 11 bshowing a top view of the thermopile carrier chip 29. This part of thefabrication process starts with etching windows 86 in the electricallyinsulating layer 81 as shown in FIG. 11 a. The location of these windows86 is such that the part of insulating layer 81 that will be forming themembrane 34 is separated from the removable beams 41 of the thermopilecarrier chip 29 (to be formed in the next step), so as to allow breakingthe removable beams 41 (as described below) without damaging themembrane 34 and/or the thermocouples. In a next step, not illustrated inthe drawings, part of the substrate 80 is etched from the back side tocreate a silicon carrier frame comprising sides 33 and removable beams41, on which a part of electrically insulating material 81 remains. Inthis way a membrane 34 is created by the electrically insulating layer81, with no substrate underneath in between sides 33 of the carrierframe and separated from the removable beams 41 (FIG. 11 b). For thesake of clarity, the electrically insulating layer 81 is shown in FIG.11 b in a different way on the carrier frame (pattern with 45° lines)and in between the sides of the carrier frame, where the electricallyinsulating layer 81 forms the membrane 34 (pattern with dots). At thispoint, Part II of the fabrication process finishes and a thermopilecarrier chip 29 is obtained.

In another embodiment of the fabrication process, grooves 87 may beformed at the back side of the frame as shown in FIG. 12 (side view).This allows for easy and well controlled breaking of the removable beams41 of the frame, e.g. after installing the thermopile carrier chip 29 ina TEG, such that the frame cracks on the grooves and such that a wellcontrolled shape is obtained as shown in FIG. 13, as opposed to what isshown in FIG. 8 b. The grooves may be formed by etching. Etching of thegrooves may be performed simultaneously with etching the bulk siliconwhile creating the carrier frame. For the sake of simplicity, in FIG. 13the electrically insulating layer 81 is shown as different elements onthe carrier frame and on the membrane (as described in relation withFIG. 11 b). The electrically insulating layer 81 may either stay in afinal device or it may be removed in a further step of the fabricationprocess, i.e. for forming membrane-type or membraneless-type devices,respectively. Etching of the windows 86 may be performed in Part I ofthe manufacturing process as well. The grooves 87 may also be fabricatedusing other techniques than etching methods, e.g. by pre-dicing.

Bulk etching of the substrate from the back side for creating a siliconcarrier frame (Part II) may be performed using different technologies,resulting in different profiles of the carrier frame. FIGS. 14 a to 14 cshow the cross section of the thermopile carrier chip 29 according tothe line I-I′ shown in FIG. 11 b when the etching is performed usinganisotropic etching (FIG. 14 a), isotropic etching (FIG. 14 b), and DeepReactive Ion Etching (DRIE) (FIG. 14 c), respectively. In case of DRIE,the etch slope may be varied from the vertical one as shown in FIG. 14 cto a slope less than the one shown in FIG. 14 a. As described inrelation with FIG. 12, grooves 87 may be etched at the back side of thecarrier frame, e.g. simultaneously with etching the bulk silicon forcreating the carrier frame. Such grooves 87 are not visible in the crosssections of FIGS. 14 a to 14 c, as these grooves are formed in the sides33 of the carrier frame at a location where windows 86 have been etchedin the electrically insulating layer 81.

Part III of the fabrication process of the TEG 40 starts with mountingthe thermopile carrier chip 29 or thermopile carrier chips 29 into a TEG40. This may be done in two different ways. The first way is to placethe thermopile carrier chip 29 or thermopile carrier chips 29 directlyinto a TEG 40 between the hot plate 37 and the cold plate 38 (FIG. 15).The second way is to assemble first a thermopile unit 50, which is thenplaced between a hot plate 37 and a cold plate 38, thereby forming a TEG40.

The first way of mounting thermopile carrier chips 29 into a TEG 40comprises first placing the thermopile carrier chips 29 between a hotplate 37 and a cold plate 38, thereby providing a good thermal contactbetween the thermopile carrier chips 29 and the plates 37, 38, forexample by using thermally conductive paste, grease, solder, glue, epoxyor any other suitable material for providing thermal joints, eitheralone or in any suitable combination. The thermopile carrier chips 29may be placed orthogonal or not orthogonal to the hot plate 37 and/orthe cold plate 38. In the example illustrated in FIG. 15, the thermopilecarrier chips 29 are placed orthogonally to both the hot plate 37 andthe cold plate 38. In the examples shown in FIG. 42 and FIG. 43, athermopile chip 30 is parallel with one of the hot or cold plates. Forclarity purposes, only one of the hot plate 37 and cold plate 38 isshown in FIG. 42 and FIG. 43. In the example illustrated in FIG. 44, athermopile chip 30 is parallel with the cold plate 38, and in aninclined position with respect to the hot plate 37. In the exampleillustrated in FIG. 45, a thermopile chip 30 is parallel with both thecold plate 38 and the hot plate 37. In the example illustrated in FIG.46, a thermopile chip 30 is in an inclined position with respect to boththe hot plate 37 and the cold plate 38. The thermopile chips 30 may bein an inclined position for different reasons, such as for example forbetter mechanical stability or better resistance to mechanical shocks orvibrations, or for example for fitting the thermopile chips in thin TEGsor in other devices. After placing the thermopile carrier chips 29between the hot plate 37 and the cold plate 38, thermally insulatingpillars 54, e.g. for supporting and thermally insulating hot and coldplates 37, 38, are installed and fixed (FIG. 15). The thermallyinsulating pillars 54 may for example be glued, preferably withthermally insulating glue, a thermoplastic or an epoxy, but other meansof mechanical attachment are also possible.

The second way for mounting the thermopile carrier chips 29 into a TEG40 is to assemble first a thermopile unit 50 which is then to be placedin between the hot plate 37 and the cold plate 38 (see also FIG. 4).There are many possible ways of doing this. For example, a thermopilecarrier chip 29 may be glued to a pillar or pillars 54 or to a wall 55made of a material with low thermal conductivity such a glass, an epoxy,or a polymer. Then, if necessary, additional thermopile carrier chips 29may be glued to each other, for example in the area of the carrierframe, and finally a second set of pillars 54 or a second wall 55 may beglued using a thermally insulating joint material 56, which may be forexample a glue, preferably thermally insulating glue, a polymer, e.g. athermoplastic, an epoxy, glass, a solder or any other material ormaterials in any suitable combination for making such joints. Theresulting thermopile unit 50 is illustrated in FIG. 16.

Upon assembling the thermopile carrier chips 29 into a TEG 40 orthermopile unit 50 as described above, the removable beams 41 of thecarrier chips are removed, e.g. broken out mechanically. FIG. 17illustrates an example of a thermopile unit 50 after removing theremovable beams 41 from the thermopile carrier chips. If the thermopileunit 50 has walls 55 or pillars 54 as in FIG. 17, the additional walls55 or pillars 54 shown in FIG. 5 in some cases may not be necessary inthe TEG 40, because these walls 55 or pillars 54 are already present inthermopile unit 50. FIG. 6 shows the thermopile chips 30 after removalof the removable beams 41 in case of not mounting the thermopile carrierships into a unit 50 first, but directly mounting them into a TEG 40.

It is clear from FIG. 6 and FIG. 17 that, after removal of the removablebeams 41, the remaining parts of the silicon frame, i.e. hot carrierpart 35 and cold carrier part 36, serve as thermally conducting pillars52, 53 and may correspond to the thermally conductive spacers asdescribed in US-2006-0000502 and U.S. Ser. No. 12/028,614, the entiredisclosure of which is incorporated herein by reference. The height ofthese thermally conducting pillars (hot carrier part 35 and cold carrierpart 36) is not limited technologically. Therefore, additional spacersin between the plates 37 and/or 38 and the thermopile chip or chips 30,as described in US-2006-0000502 and U.S. Ser. No. 12/028,614, may not benecessary. However, to decrease the cost of a technological process, thechip area per one TEG may be minimized. Therefore, it may be worth toreplace a substantial part of the hot carrier parts 35 and the coldcarrier parts 36 with an additional thermally conductive spacer 52, 53or with more than one thermally conductive spacer 52, 53, e.g. as shownin FIG. 18. In between the thermally conductive spacers 52, 53, onethermopile chip 30 or several thermopile chips 30 may be present, forexample as shown in FIG. 19.

If more than one thermopile chip 30 is used in a TEG 40 or in athermopile unit 50, the thermopile chips 30 may be grouped in couplesfacing with the same side to each other such as e.g. shown in FIG. 20.Coupling of thermopile chips 30 as shown in FIG. 20 results in anincreased thermal resistance of the air inside the TEG, and consequentlya larger temperature difference between the thermocouple hot and coldjunctions (as compared to a TEG with non-coupled thermopile chips),resulting in a higher voltage and power generated by the TEG (e.g. underconditions of non-constant heat flow and non-constant temperaturedifference). Care has to be taken to prevent electrical shorts within acouple and between couples. This is especially the case for thick filmthermopiles or micromachined thermopiles (discussed below), becausethick films may show larger stress than thin films, causing bending ofthe thermocouple legs and/or the membrane, or may have a larger surfaceroughness as compared to thin films. Therefore, an insulating layer suchas electrically insulating glue 56 or at least one electricallyinsulating spacer 57 may be placed in between the surfaces of thethermopile chips 30 that comprise thermocouples or electrical contacts.The at least one spacer 57 may be made of a layer of photoresist or anyother suitable electrically insulating material. Instead of using one ormore spacers 57, also a complete electrically insulating layer coveringthe surface of at least one of the thermopile chips 30 in each couple ofthermopile chips may be used.

It is to be understood that although preferred embodiments, specificconstructions and configurations, as well as materials, are discussedherein, various changes or modifications in form and detail may be madewithout departing from the scope and spirit of this invention. Forexample, other thermoelectric materials may be used besides BiTe orSiGe, and other materials may be used for the different elements of thedevice. The parts and their particular configurations shown in theFigures are interchangeable between the different technologies and arenot limited to the cases shown. The configurations shown in the Figuresare for illustration purposes only; the diversity of possibleembodiments is actually much greater.

The performance of a TEG 40 as described in the above embodiments may beenhanced in several ways, e.g. (i) by adding a thermally conductingspacer 52, or 53, or two spacers 52, 53 into the thermopile unit 50,further separating the thermopile chip or chips 30 from at least one ofthe plates 37 and 38. This leads to improved Rayleigh/Reynolds numbersat the surface of the cold plate according to U.S. Ser. No. 12/028,614,(ii) by varying the contact area of the TEG 40 with the heat source andthe heat sink according to US 2006-0000502 and U.S. Ser. No. 12/028,614,and (iii) by appropriately selecting the materials and the design inorder to obtain the desired thermal isolation between the hot plate 37and the cold plate 38. These possibilities are described in US2006-0000502 and U.S. Ser. No. 12/028,614, the entire disclosure ofwhich is incorporated herein by reference.

Hereinafter, additional possibilities to enhance the performance of thethermopile chip 30 and TEG 40 will be discussed for a TEG 40 attached toa human being. However, this is only by means of an example and thus isnot limiting the present invention, which is applicable for all ambientheat sources and heat sinks with high thermal resistance, i.e. with lowthermal conductivity, such as for example endotherms or for materialsused in building construction, for example bricks and glass.

When placing a TEG 40 on a human body, there is a small temperaturedifference between the hot junctions and the cold junctions of thethermocouples, i.e. several degrees Celsius or less. Therefore a largenumber of thermocouples (thousands of thermocouples) may be required toproduce a voltage of at least 0.7-1.5 V as needed for poweringaccompanying electronics. However, because of user comfort, such TEGsmay be limited in size and often also limited in thickness. The usefulpower (e.g. microwatt to milliwatt level) may then be obtained with amembrane-type TEG using narrow (several μm wide) thermocouple legs.However, narrowing the legs results in a high electrical resistance ofthe TEG (many mega-ohms), and therefore such a TEG may become uselessfor practical applications. If, however, the length of the membrane(i.e. the size of the membrane along the thermocouple lines) is madesmall enough to decrease the electrical resistance of the TEG, theresulting parasitic thermal conductance through the air in between theplates 37, 38 increases and it thermally shunts the thermopiles,resulting in low voltage and power. These are the main reasons thatmembrane thermopiles have not previously been practical. The presentdisclosure offers a solution to this problem, by making thermal shuntson the membrane, such that the distance between the hot carrier part 35and the cold carrier part 36 remains large, but the length of thethermoelectric part 31 is smaller, thereby decreasing the electricalresistance of the thermocouples and increasing the produced voltage andpower as compared to a membrane TEG without thermal shunts. FIG. 13shows a thermopile chip 30 in which the length of the thermoelectricpart 31 of the thermocouple lines is approximately equal to the lengthof the membrane 34. FIGS. 6 and 8 b show the more advantageous design,where the electrically conductive interconnects 32, e.g. metal lines,extend to the central part (i.e. the part in the centre between the hotcarrier part 35 and the cold carrier part 36) of the membrane 34. In theexamples shown in FIGS. 6 and 8 b the length of the thermoelectric part31 of the thermocouple lines is smaller than the length of the membrane34. The parasitic thermal conductance through the air increases alittle, but despite of this, the voltage and the power may increasesignificantly. The effect of thermal shunts is shown in FIG. 21. Most ofthe available thermal gradient appears on the relatively smallthermoelectric part 31 when using thermal shunts 32, 85. It is clearthat the methods of manufacturing reported above are fully applicable tothis thermopile design.

In a preferred embodiment, the thermal shunts 90 are fabricated in sucha way that the electrical resistance of the shunts between the adjacentthermocouple legs 11, 12 is minimised through minimising the electricallength of the shunts, as shown in FIG. 22. For comparison, FIG. 8 billustrates another embodiment, wherein the electrical resistance of thethermal shunts is not minimised.

The thermal shunts 90 as shown in FIG. 22 perform two independentfunctions at once, i.e. electrical connection between the thermoelectricparts 31 and thermal connection of the thermoelectric parts 31 with thesides 33 of the carrier frame. These two functions may be split into twoseparate elements, i.e. a thermally conductive thermal shunt 90 and anelectrically conducting interconnect 32, as shown in FIG. 23. Thefabrication process stays generally the same. Only one fabrication stepis added: deposition and patterning of the thermal shunt layer 90, whichis performed in between Part I and Part II of any of the fabricationprocesses described above. An advantage of this design and technology isthat the thermally conductive shunt 90 may have larger thermalconductivity as compared with a thermal shunt made of the same material(metal) as the interconnects 32. The material for the thermal shunt 90may then be chosen from a large family of thermally conductive materialsirrespective of their electrical conductivity, such as for examplepyrolytic graphite, diamond or silicon carbide. This improves thegenerated voltage and the power.

If the material selected for the thermal shunts 90 is not electricallyconductive, then the space in between the thermal shunts 90 may bereduced to zero as shown in FIG. 24, thereby improving the voltage andthe power.

If the material selected for the thermal shunts 90 is not electricallyconductive, the insulating layer 81 may not be necessary on a part ofthe structure between the sides 33 or on the whole structure (as will beshown below in FIGS. 26 c and 26 d), and the layer 90 may performfunctions of the membrane 34, as shown in FIG. 25.

If the stiffness and thickness of the film 82 of a first thermoelectricmaterial, the film 84 of a second thermoelectric material and the film85 of interconnection material are sufficient to hold the structure,i.e. if the structure is self-supporting, the insulating layer 81 maynot be necessary. This results in a membrane-less thermopile chip 30, asillustrated in FIG. 26 a (side view) and FIG. 26 b (top view). As onecan see, the membrane function is shared between thermal shunting layer90 and the layers 82, 84, and 85. Moreover, there may be holes inbetween the thermoelectric parts 31, and/or in between the interconnectlines 85, thereby further improving the voltage and power output. Themembrane-less thermopile chip 30 may also be made with thermal shunts asin FIGS. 8 b, 11 b, 13, and 22. A membrane-less thermopile chip 30 maybe manufactured with a slightly modified fabrication process as comparedto a membrane-type thermopile chip 30 (described above). Either thedeposition of an electrically insulating layer 81 may be omitted fromPart I of the manufacturing process, or an electrically insulating layer81 may be provided as described above and may then be removed at leastbetween the sides 33 of the carrier frame at the end of Part II of themanufacturing process. The electrically insulating layer 81 is used onthe sides 33 if these sides are electrically conductive, as shown inFIG. 26 c. However, if the sides 33 themselves are made of electricallyinsulating material, the electrically insulating material 81 is notrequired at all, as in the example shown in FIG. 26 d. In some cases, avery thin, e.g. 50-100 nm membrane may still be used for technologicalreasons, for example as an etch stop for etching in Part II of thefabrication process.

The invention is not limited to the shown examples and embodiments, anda much wider spectrum of membranes or membrane structures may beproposed. For example, a doped n-layer of silicon on top of a p-typewafer may serve as an etch stop barrier, e.g. for KOH. Then, a part 94of a substrate, more in particular a layer with a different type ofdoping as compared to the bulk of the substrate, may serve as a thermalshunt as shown in FIG. 26 e.

Despite the better power and voltage obtainable in the structuresaccording to FIGS. 25 to 26 e, as compared with the thermopile chip 30comprising a membrane 34 made of an electrically insulating material(FIGS. 21 to 24), the latter version is considered to be preferable fora first implementation of TEGs 40 in factories for mass production. Thisis due to (i) the smaller number of technological steps required, whichmay result in a better performance/cost ratio and a lower cost, and (ii)the better mechanical stiffness due to the presence of one non-segmentedmembrane 34, which may provide better reliability and therefore anextremely long life time of the thermopiles in customer products.

In some cases, optimising the thermoelectric and/or thermal and/orelectrical properties of the first thermoelectric material comprised inlayer 82 on one hand and of the second thermoelectric material comprisedin layer 84 on the other hand, may require different fabricationparameters to obtain the best properties for both materials. Forexample, different annealing temperatures may be used for p-type BiTeand n-type BiTe. Therefore, the fabrication of p-type and n-typethermocouple legs on one substrate results in competing considerationsin determining the annealing temperature. In order to obtain optimumperformance for both p-type and n-type thermoelectric layers, e.g.tellurium-containing thermoelectric layers, separate n-type and p-typecarrier chips 29 may be fabricated, as illustrated in FIG. 27 and FIG.28. The two thermopile carrier chips 29 of FIG. 27 and of FIG. 28 thenmay be coupled and attached face-to-face to each other, e.g. usingwafer-to-wafer or chip-to-chip bonding. This is illustrated in FIG. 29,where the front thermopile carrier chip 29 is shown transparent for thesake of clarity. For example, reflow of indium bumps 95 may be used forthe electrical interconnection of an n-type chip and a p-type chip witheach other. In order to obtain a good reliability of the chip-to-chipinterconnects, indium bumps may be created on both p-type and n-typethermopile carrier chips 29. The thermopile carrier chips 29 may bearranged in a thermopile unit 50 or in a TEG 40 as shown in FIG. 20.

Breaking the removable beams 41 of the carrier frame in a TEG 40 or in athermopile unit 50 may not be necessary if other means are selected toremove them. Examples of other methods that may be used for removing theremovable beams 41 are standard dicing, other mechanical cuttingmethods, laser dicing, or wet etching (e.g. by immersing removable beams41, side by side, into an etching solution). However, breaking the sidesof the carrier frame along the grooves 87 (FIG. 12) is considered as aparticularly advantageous manufacturing method.

A further example of a method for eliminating the removable beams 41 isdescribed below. After performing Part I of the fabrication process, thethermopile wafer 28 may be diced into thermopile dies such as shown inFIG. 30. Then, thermally isolating pillars 54 may be formed against thesides of the thermopile dies (FIG. 31 a) or may be attached, e.g. gluedor soldered, thereto using thermally insulating interconnecting material100 (FIG. 31 b). If the material of pillars 54 and of interconnectingmaterial 100 is resistant to the etchant used for etching the substrate80, then Part II of the fabrication process can be performed asdescribed above. If however the material of pillars 54 and/or ofinterconnecting material 100 is not resistant to the etchant used foretching the substrate 80, then all surfaces coming into contact with theetchant during Part II of the fabrication process may be protected withetch-resistant coatings or layers. The thermopile die after Part II ofthe fabrication process looks for example as shown in FIG. 31 a or FIG.31 b. The use of pillars 54 on each thermopile die does not exclude theuse of additional pillars 54 or walls 55 in a thermopile unit 50 or in aTEG 40. An advantage of such an approach, i.e. an approach wherein theremovable beams 41 are diced and not broken from the carrier frame, isthat opening of the windows 86 is not needed, which decreases the numberof lithographic steps required. In the approach where the removablebeams 41 are broken from the carrier frame, opening of windows 86 may beperformed in order to avoid damaging the membrane and/or thethermocouples during breaking.

In Part II of the fabrication process, etching of windows 86 in themembrane 34 may not be necessary if the membrane is separated from thesides 41, for example by laser cutting of the membrane. This isillustrated in FIG. 32, showing an example of cutting lines 101. Othermethods than laser cutting may be used, such as for example cuttingusing a diamond cutting tool. An example of a thermopile chip 30 aftercompleting such a fabrication process, i.e. after removing the removablebeams 41 and the parts of the electrically insulating layer 81 whichhave been cut lose, is shown in FIG. 33.

In order to quantify the performance of the TEG 40, calculations havebeen performed for a TEG 40 comprising membrane-type thermopile chips 30of the two different versions shown in FIG. 13 and in FIG. 22, i.e.without thermal shunts (FIG. 13) and with thermal shunts (FIG. 22),respectively. It is assumed that the TEG is on a human wrist indoors(i.e. with no wind). Moreover, the person is supposed to be sitting. Thecalculations are performed for bismuth telluride thermopile chips of10×28 mm² size with an etch profile as shown in FIG. 14 a. A standard8-inch microelectronic process is chosen for manufacturing thethermopile chips 30, wherein the substrate is made of 0.725 mm-thicksilicon. It is assumed that the cold plate 38 has a size of 3×3 cm² andthe hot plate has a size of 2×3 cm². The plates 37, 38 have a thicknessof 0.5 mm each, so the size of the TEG 40 is 3×3×1.1 cm², i.e. similarto the size of a watch. The thermal shunts 90 and electricalinterconnects 32 are assumed to be fabricated of 2 μm thick aluminium.The air temperature is 22° C. The thermal resistance of the body at anair temperature of 22° C. is assumed to be 150 cm²K/W on a human wristnear the radial artery. An output voltage of at least 5 V is assumed asmajor requirement for the TEG, to be sure that the TEG still produces atleast 2 V at an ambient temperature of 30° C. Calculations have beenperformed for different cases.

Case 1: without thermal shunts (FIG. 13). A 3 μm thick film of BiTe isused for forming the layers of thermoelectric material. In the TEG, 14thermopile chips are coupled into 7 couples in a way similar to the oneshown in FIG. 20, face to face on a couple by couple basis. A goodelectrical contact resistance of 10Ω·μm² between the interconnectionmetal and the thermoelectric material is assumed. The dependence of thepower produced by the TEG on the length of the thermocouple legs (or ona membrane length which is the same in the case considered here) at suchconditions is shown in FIG. 34.

Case 2: without thermal shunts (FIG. 13). A 1 μm thin film of BiTe isconsidered, to obtain a 3-fold decrease of the film deposition time ascompared to Case 1. In the TEG, 10 thermopile chips are coupled into 5couples in a way similar to the one shown in FIG. 20, face to face on acouple by couple basis. As compared to Case 1, this results in adecrease of the production cost per TEG. A moderately good electricalcontact resistance of 100Ω·μm² between the interconnection metal and thethermoelectric material is assumed. The dependence of the power producedby the TEG on the length of the thermocouple legs (or on the membranelength which is the same in the case considered here) at such conditionsis shown in FIG. 35.

Case 3: with thermal shunts (FIG. 22). In this case the length of thethermocouple legs is less than the length of the membrane. A 3 μm thickfilm of BiTe is used for forming the layers of thermoelectric material.The TEG comprises 14 thermopile chips and a contact resistance of10Ω·μm² between the interconnection metal and the thermoelectricmaterial is assumed, as in Case 1. The dependence of the power producedby the TEG on the length of a membrane is shown in FIG. 36 for a 0.5mm-long thermocouple leg. The dependence of the power produced by a TEGwith a 3.8 mm-long membrane on the length of the thermocouple legs isshown in FIG. 37.

Case 4: with thermal shunts (FIG. 22). A 1 μm thin BiTe film is assumed,10 thermopile chips are used, and an electrical contact resistance of100Ω·μm² between the interconnection metal and the thermoelectricmaterial is assumed. The dependence of the power on the length of themembrane is shown in FIG. 38 for 0.31 mm-long thermocouple legs. Thedependence of the power with a 2.4 mm long membrane on the length of thethermocouple legs is shown in FIG. 39.

Summarizing the results of Cases 1 and 2, an output power between 15 μWand 40 μW can be obtained with thermopile chips 30 without thermalshunts (as in FIG. 13), depending on the thickness of the BiTe film andthe contact resistance between the interconnection metal and thethermoelectric material. As can be seen by comparing cases 1 and 3 orcases 2 and 4 with each other, the power increases when thermal shuntsare used in the design, and this improvement is not related toparticular values of the thermoelectric layer thickness and/or thecontact resistance between the interconnection metal and thethermoelectric material. Further increase of the thermoelectric layerthickness results in a TEG performance similar to the best performancesof micromachined thermopiles according to US-2006-0000502 or of othertypes of thermopiles according to U.S. Ser. No. 12/028,614.

Hereinafter, specific designs of thermopile chips 30 are discussed forapplication in small (e.g. few centimeters and less) or thin (e.g.several millimeters) devices such as for example wireless sensor nodes.An appropriate device to be used as an example is a watch 110, beingself-powered, for example by a TEG 40. Of course, all TEGs 40 andthermopile units 50 discussed above may be implemented into a watch,e.g. as shown in FIG. 40, when a special watch body is fabricated, or asshown in FIG. 41 for a more “classical” watch shape. The numbers inthese simplified cross sections of a watch denote the following items:111 is a watch body; 112 is an optically transparent front lid; 113 is abackside lid; 114 is a watchstrap; 115 are all watch components thatcould be referred as to “hot parts”, equivalent to a hot plate 37; 116are all watch components that could be referred as to “cold parts”,equivalent to a cold plate 38, wherein the zone 116 may also includeelements specially shaped as a fin or pin radiator; and 117 is a thermalinsulation which may include components made of thermally insulatingmaterials or which may include compartments filled with gases atdifferent pressure or under vacuum. As a further example, the TEG 40shown in FIG. 41 is split in two sub-units each comprising a pluralityof thermopile chips 30, both sub-units being electrically connected inseries. The sub-units are representing one TEG composed of 8 thermopilechips 30. This splitting into sub-units may be done to fit the availablespace in a watch. The invention is not limited by the examples shown,and any other arrangement is possible which provides enough power andvoltage to power the watch (or any other self-powered device). However,the problem of fitting a TEG 40 into a thin or a small-size watchremains. Therefore reduction of the size of a TEG 40 and/or of athermopile unit 50 is desirable to fit the available volume in a watch.In advanced wrist devices, more and more functionalities will be added,making it a personal assistant, adviser, security/safety/emergency andhealth monitoring device, personal ID tag, messenger, mobile phone (withlimited call duration), GPS, etc. Therefore, the volume available for anenergy scavenger will always be an issue. A TEG 40 then can beincorporated into a watchstrap as an insert into it and it may be forcedto be located on a radial or ulnar artery through its design.

In certain applications there may be a desire for TEGs 40 with athickness that is as small as possible. In order to decrease thethickness of a TEG 40 and/or of a thermopile unit 50, the thermopilechip or chips 30 may be placed parallel to at least one of the hot plate37 and/or the cold plate 38, as shown in FIGS. 42-45. Alternatively, thethermopile chips 30 may be otherwise inclined, but preferably moreparallel than perpendicular to the hot plate 37 and the cold plate 38,as shown in FIG. 46. This TEG arrangement generates a lower output poweras compared to the above configurations wherein the thermopile chips 30are perpendicular to at least one of the hot plate 37 and/or the coldplate 38. However, this approach allows a much more compact design of aTEG 40 and a thermopile unit 50, while still providing reasonably goodoperation at very small temperature differences between the heat sourceand the heat sink.

Future self-powered devices on a human body should not only produce themaximal output power at normal air temperatures like e.g. 22° C. orless, but they may be optimized for the temperature range of theiroperation. At about 36-37° C. air temperature, the performance of anyTEG on a human body dramatically deteriorates due to the extremely lowtemperature difference between the skin temperature and the air. Thesame is valid for any technical application of TEGs, when thetemperature difference between the hot plate 37 and the cold plate 38becomes very small. Therefore, a TEG 40 for application in a watch maybe optimised in such a way that the non-operational range of airtemperatures which takes place around a temperature of human skin is assmall as possible.

Examples of TEG designs for miniature devices are shown in FIGS. 42-46.The manufacturing technology is not affected by changing the design. Asshown in FIGS. 42-46, thermally insulating elements (pillars, walls,etc.) 120 may be introduced in a TEG 40. These thermally insulatingelements 120 can be installed in between the hot plate 37 or/and coldplate 38 and a carrier frame 33 and may be used for additionalmechanical support. Thermally insulating elements 120 shaped as pillarsare shown in FIGS. 42, 44, 46; thermally insulating elements 120 shapedas a wall are shown in FIGS. 43, 45. The shape of plates 37, 38 and theinsulating elements 120 may be very different. The thermally insulatingelements 120 may be used temporarily, only during assembling the device,or permanently, left in the final device. However, the elements 120 arepreferably removed upon assembling the TEG 40 or thermopile unit 50. TheTEG 40 may contain several thermopile chips 30, for example connectedelectrically in series and thermally in parallel. However, otherconfigurations are possible, such as for example a combination ofseries/parallel connections, electrically or thermally or bothelectrically and thermally.

In many practical cases, wherein the thermopile chips 30 are mountedparallel to the plates 37, 38 or inclined with respect to the plates 37,38, there may be no need for separating, e.g. dicing, the thermopilechips from each other, e.g. as shown in FIG. 47. As an example, thethermopile chip 30 shown in FIG. 47 comprises four rows of thermocouplesbeing connected electrically in series. The electrical connections inbetween rows of thermocouples may be done on chip, e.g. as shown in FIG.47. Adjacent rows of thermocouples may share a hot carrier part 35 or acold carrier part 36. Hot and cold carrier parts 35, 36 can beinterchanged as compared to what is shown in FIG. 47. Mounting athermopile chip 30 according to FIG. 47 in a thermopile unit 50 or in aTEG 40 may be done for example as illustrated in FIGS. 48 a-c, resultingin a thermally parallel connection of the thermocouple rows.

In FIG. 48 a-c, an example is shown of an assembling procedure for anarrangement of a thermopile chip 30 as shown in FIG. 47 parallel to theplates 37, 38. Assembling may start from any of the plates 37, 38. As anexample, shown in FIG. 48 a, thermally insulating elements 120 areinstalled on a hot plate 37. Then, the thermopile carrier chip 29, e.g.a thermopile carrier chip comprising rows of thermocouples (as e.g.shown in FIG. 47) is installed and thermally attached with any meansdiscussed above. The removable beams 41 are then removed using any ofthe ways described above. FIG. 48 a shows the assembly after removingthe removable beams 41. Then, the cold plate 38 is mounted as shown inFIG. 48 b and thermally attached with any means described above. At thisstage of assembling, the device is ready for being used. However, if theposition of the plates 37, 38 is fixed with respect to each other, e.g.with pillars 54 or walls 55, or if the product wherein the TEG 40 isused provides fixation of plates 37, 38 with respect to each other, thenthe thermally insulating elements 120 may be removed. The TEG 40 maythen for example look as shown in FIG. 48 c.

FIG. 49 shows an example of a TEG 40 filled with a thermal insulationmaterial 51, such as for example a nanoporous material. Several ways ofputting thermal insulation 51 are shown at once: with gaps, and withoutgaps.

All other innovations discussed in this patent application areapplicable to the parallel arrangement of thermopile chips (parallel toplates 37, 38). For example, the coupled thermopile chips 30 as shown inFIG. 20, or the embodiment shown in FIGS. 27-29 may be used. An exampleof a possible arrangement is shown in FIG. 50, where the number ofthermopile chips 30 can be different. Also, whenever the Figures referto a membrane 34, it may be clear that the membrane-less thermopiles asdisclosed above are also possible and an indication of a membrane indrawings is only for easier explanation and just for the sake ofclarity.

An example of a TEG 40 with parallel arrangement of thermopile chips 30(i.e. parallel to plates 37, 38) is shown in FIG. 51, for application ina watch, where the parts of a watch body 115, 116 play the role of thehot plate 37 and the cold plate 38, respectively. Such parallel-arrangedthermopile chips may be easily embedded into thin devices and garmentlike e.g. a wrist or head strap, belt, cap, and clothes, glasses andearphones, jewelry such as a necklace or a bracelet, and into thinportable devices.

To minimize the radiation heat exchange inside a TEG 40, all innersurfaces of the TEG 40 may have low emissivity (lower than 20%,preferably lower than 10%) in the infrared region of the electromagneticspectrum. For example, a number of metals may serve as low-emissivitymaterials. Thus, if plastics or other materials used for forming the TEG40 have large emissivity, they preferably may be covered with highlyreflecting (low emissivity) material, such as for example a metal. Thethermal shunts and/or interconnects covering a large part of themembrane of the proposed thermopile chips also may help to minimize theradiation heat exchange to/from the membrane and direct heat exchangebetween the plates 37 and 38 because the metal layer has a largereflection coefficient and a low emission coefficient.

As the TEG 40 may also be used for outdoor applications at temperaturesabove body core temperature and with a radiant heat from sun or fromambient, the TEG 40 may be used in reverse mode of operation, i.e. whenthe heat flow direction is from the ambient into a body, or to anothersurface, on which the device is mounted.

Thermal shunts 90 as described in the present disclosure may also beused in other types of thermopiles or thermoelectric generators than themembrane-type and membrane-less type devices described above. Forexample, thermal shunts 90 may advantageously be used in thermopiles orthermoelectric generators comprising micromachined thermocouples, suchas for example described in US-2006-0000502 and U.S. Ser. No.12/028,614. This is illustrated in FIGS. 52 to 56.

FIG. 52 shows part of a micromachined thermopile chip 140 (only onethermocouple is shown), wherein thermal shunts 90 made of a thermallyand electrically conducting material such as e.g. a metal are provided.Thermal shunts 90 may be provided on the cold side and/or on the hotside of the thermocouple legs. In the example shown, the thermocouple isfabricated on a thermopile die 46, e.g. hot die 46. A die 45, e.g. colddie 45, is attached to the thermocouples using solder bumps 143, whichare fabricated on top of metal pads 142. In the example shown, the diesmay for example be manufactured on silicon wafers. In this caseelectrically insulating but thermally conducting layers 141 may beformed on the dies. Layers 141 may not be needed if the material of thedies 45, 46 is electrically insulating.

FIG. 53 and FIG. 54 show part of another micromachined thermopile chip140 (only one thermocouple is shown) comprising thermal shunts 90 madeof a thermally and electrically conducting material such as e.g. ametal. Thermal shunts 90 may be located on the hot side (as in FIG. 53),on the cold side or on both sides (as in FIG. 54) of the thermocouplelegs. However, other locations, such as e.g. in the central part of thethermocouple legs are possible. Dies 45 and 46 may be attached to thethermopile using a thermally conducting and electrically insulatingmaterial 145 such as glue. For example, an epoxy layer with thermalconductivity of 0.006 W/cm·K or more, or a photoresist can be used forforming layer 145.

FIG. 55 shows another example, wherein thermal shunts 90 are provided onboth the hot and cold side of the thermocouples. In addition, die 45comprises bumps or pillars 145 to increase an average distance inbetween dies 45 and 46, which is similar to the raised elongatedstructures as disclosed in US-2006-0000502.

Yet another example of a thermal shunt 146 is illustrated in FIG. 56. Itcomprises several micrometer-thick thermal shunts 146 performing alsothe function of a metal layer interconnect 13. One or more thermalshunts 90 can still be useful on one or more legs and/or on one or moresides of the thermocouple legs. As an example, in FIG. 56 a shunt 90 isonly present on first thermocouple leg 11 but not on second thermocoupleleg 12.

1. A method of manufacturing a thermopile carrier chip comprising aplurality of thermocouples, the method comprising: on a first surface ofa first substrate comprising a first material, providing a plurality offirst-type thermocouple legs; thereafter removing part of the firstmaterial from a second surface opposite to the first surface to form afirst carrier frame from the first substrate, the first carrier framecomprising a first hot carrier part, a first cold carrier part, andfirst removable beams, wherein the first hot carrier part, the firstcold carrier part, and the first removable beams comprise a contiguousstructure made of the first material, and wherein the first-typethermocouple legs are at least partially released from the firstmaterial of the first substrate, the first-type thermocouple legs beingattached between the first hot carrier part and the first cold carrierpart; and electrically connecting the plurality of first-typethermocouple legs with a plurality of second-type thermocouple legs,thereby forming an electrical series connection of alternatingfirst-type thermocouple legs and second-type thermocouple legs.
 2. Themethod according to claim 1, wherein electrically connecting theplurality of first-type thermocouple legs with a plurality ofsecond-type thermocouple legs comprises: on the first surface of thefirst substrate, providing a plurality of second-type thermocouple legs.3. The method according to claim 1, wherein electrically connecting theplurality of first-type thermocouple legs with a plurality ofsecond-type thermocouple legs comprises: on a first surface of a secondsubstrate, providing a plurality of second-type thermocouple legs; andthereafter removing part of the second substrate from a second surfaceopposite to the first surface to form a second carrier frame from thesecond substrate, the second carrier frame comprising a second hotcarrier part, a second cold carrier part, and second removable beams,wherein the second-type thermocouple legs are at least partiallyreleased from the second substrate, the second-type thermocouple legsbeing attached between the second hot carrier part and the second coldcarrier part.
 4. The method according to claim 2, further comprising,before providing the plurality of first-type thermocouple legs on thefirst surface of the first substrate, providing an electricallyinsulating membrane layer onto the first surface of the first substrate.5. The method according to claim 4, further comprising separating themembrane layer from the first removable beams.
 6. The method accordingto claim 5, wherein separating the membrane layer from the firstremovable beams comprises providing windows in the membrane layer. 7.The method according to claim 5, wherein separating the membrane layerfrom the first removable beams comprises cutting of the membrane layer.8. The method according to claim 2, further comprising providing atleast one thermal shunt for thermally connecting at least one side ofthe plurality of thermocouples to at least one of the carrier parts. 9.The method according to claim 1, further comprising: assembling thethermopile carrier chip into a thermopile unit; and removing the firstremovable beams.
 10. The method according to claim 9, wherein assemblingthe thermopile carrier chip comprises attaching the thermopile carrierchip to a thermally insulating structure.
 11. The method according toclaim 9, wherein assembling the at least one thermopile carrier chipcomprises providing at least one thermally conductive spacer thermallyconnected to at least one of the carrier parts.
 12. The method accordingto claim 2, further comprising: providing the thermopile carrier chipbetween a hot plate and a cold plate.
 13. The method according to claim12, further comprising: providing at least one thermally insulatingstructure between the hot plate and the cold plate.
 14. The methodaccording to claim 12, wherein the thermopile carrier chip or thermopileunit is placed parallel to the hot plate.
 15. The method according toclaim 12, wherein the at least one thermopile carrier chip or thermopileunit is placed parallel to the cold plate.
 16. A method of manufacturinga thermopile carrier chip comprising a plurality of thermocouples, themethod comprising: on a first surface of a first substrate comprising afirst material, providing a plurality of first-type thermocouple legs;thereafter removing part of the first material from a second surfaceopposite to the first surface to form a first carrier frame from thefirst substrate, the first carrier frame comprising a first hot carrierpart, a first cold carrier part, and first removable beams, wherein thefirst hot carrier part, the first cold carrier part, and the firstremovable beams comprise a contiguous structure made of the firstmaterial, and wherein the first-type thermocouple legs are at leastpartially released from the first material of the first substrate, thefirst-type thermocouple legs being attached between the first hotcarrier part and the first cold carrier part; electrically connectingthe plurality of first-type thermocouple legs with a plurality ofsecond-type thermocouple legs, thereby forming an electrical seriesconnection of alternating first-type thermocouple legs and second-typethermocouple legs; and providing at least one thermal shunt forthermally connecting at least one side of the plurality of thermocouplesto at least one of the carrier parts.